Thoughts on Perl and Emacs, technology and writing

Code Reuse and ProcessMutex

I’m a huge fan of code reuse, and I tend to trust other people’s public code more than my own private code. After all, if they put effort into making it public, they must have put a lot of thought into it. And more than likely it is probably their speciality. That’s why I don’t (for example) implement my own webservers 🙂 Having said that, I’ve reimplemented more wheels than I care to admit. Here is me, providing my own version of identity – a built-in emacs function. How embarrassing. Almost put me off blogging that did.

So, I try to do a bit of due dilligence when I’m thinking about writing a simple thing that someone surely has already done. What I want, is an interprocess mutex. There must be a million ways of doing these things, so I have a quick look on CPAN. Searching for mutex brings up LockFile::NetLock which looks interesting (although slightly paranoid, and I don’t have my own ftp server).

dmake.EXE: Error code 129, while making 'Semaphore.o'
MJP/POSIX-RT-Semaphore-0.05.tar.gz
C:\strawberry\c\bin\dmake.EXE -- NOT OK
Running make test
Can't test without successful make
Running make install
Make had returned bad status, install seems impossible

Yep, I was right. I’ll spare you the results from the other hour I spent googling various things like semaphore and process mutex.

Okay, let’s think about this. Maybe I could write my own simple little thing with a nice API, and if I find a decent module later I can delegate to it, or maybe delegate to Win32::Semaphore on Windows and the SysV version everywhere else. The ACE guys call that a wrapper facade. Does flock work on Windows?

So the plan is to call flock LOCK_EX on a file in the constructor, and then flock LOCK_UN in the destructor in a kinda RAII way. Famous last words, but what else could I possibly need?